The present invention relates to a thermal image receiving sheet, more particularly to a thermal transfer image receiving sheet which is capable of providing a full color image having a high quality without a color dropout, etc.
Heretofore, various thermal transfer methods have been known. Among these, there has been proposed a method wherein a sublimable dye (or subliming dye) is used as a recording agent, and is carried on a substrate sheet such as paper and plastic film to obtain a thermal transfer sheet, and various full color images are formed on an image receiving sheet such as paper and plastic film having thereon a dye receptor layer, by using the resultant thermal transfer sheet.
In such a case, a thermal head of a printer is used as heating means so that a large number of color dots of three or four colors are transferred to the image receiving sheet under heating in a very short period of time. As a result, a full color image of an original is reproduced by using the multi-color color dots.
The thus formed images are very clear and are excellent in transparency, since the dyes are used therein as a colorant. Accordingly, these images are excellent in half tone reproducibility and gradation characteristic, and are substantially the same as the images formed by the conventional offset printing and gravure printing. Further, when the above image forming method is used, there can be formed images of high quality which are comparable to full color photographic images.
In order to effectively carry out the thermal transfer method as described above, not only the structure of the thermal transfer sheet but also the structure of the image receiving sheet on which an image is to be formed is important. More specifically, at the time of the formation of the image, both of the thermal transfer sheet and the image receiving sheet are conveyed in a printer to be used for such image formation, and both of these sheets are rubbed with each other. As a result, the image receiving sheet may generally be charged and foreign substance such as dust is attached to the dye receiving surface of the image receiving sheet on the basis of the above charging, whereby a problem such as color dropout is posed. In general, it is necessary to solve such a problem by subjecting the thermal transfer sheet and/or the image receiving sheet to an antistatic treatment. For example, Japanese Laid-Open Patent Application (JP-A, KOKAI) No. 56489/1988 discloses a thermal transfer image receiving sheet wherein the surface of a dye receiving layer provided on one side surface of a substrate sheet is subjected to an antistatic treatment. However, in a case where a full-color image is intended to be formed by use of a thermal transfer system, since the same region of the dye receiving layer is subjected to the dye transfer operation three to four times, a sufficient antistatic property cannot be maintained when an antistatic agent is simply applied onto the dye receiving surface of the thermal transfer image receiving sheet. As a result, the above problem is not sufficiently solved and therefore a full-color image of high quality free of the color dropout has not been formed yet. Such a problem is posed not only in the case of a thermal transfer image receiving sheet to be used in combination with a thermal transfer sheet of a sublimable dye type, but also in the case of a thermal transfer image receiving sheet to be used in combination with a thermal transfer sheet of a melt transfer type.